VecView behaviour

[Andreas Grassl]

Barry Smith schrieb:
> 
>   When properly running nn-cg (are you sure everything is symmetric?)
> should require 10-30 iterations (certainly for model problems)

ok, this was the number I expected.

> 
>> nn-cg on 2 nodes 229 iterations, condition 6285
>> nn-cg on 4 nodes 331 iterations, condition 13312
> 
>   Are you sure that your operator has the null space of only constants?

no, I didn't touch anything regarding the null space since I thought it would be
done inside the NN-preconditioner. Does this mean I have to set up a null space
of the size of the Schur complement system, i.e. the number of interface DOF's?

cheers,

ando

> 
>     Barry
> 
> 
> On Jun 3, 2009, at 5:29 AM, Andreas Grassl wrote:
> 
>> Barry Smith schrieb:
>>>   Hmm, it sounds like the difference between local "ghosted" vectors
>>> and the global parallel vectors. But I do not understand why any of the
>>> local vector entries would be zero.
>>> Doesn't the vector X that is passed into KSP (or SNES) have the global
>>> entries and uniquely define the solution? Why is viewing that not right?
>>>
>>
>> I still don't understand fully the underlying processes of the whole PCNN
>> solution procedure, but trying around I substituted
>>
>> MatCreateIS(commw, ind_length, ind_length, PETSC_DECIDE, PETSC_DECIDE,
>> gridmapping, &A);
>>
>> by
>>
>> MatCreateIS(commw, PETSC_DECIDE, PETSC_DECIDE, actdof, actdof,
>> gridmapping, &A);
>>
>> and received the needed results.
>>
>> Furthermore it seems, that the load balance is now better, although I
>> still
>> don't reach the expected values, e.g.
>> ilu-cg 320 iterations, condition 4601
>> cg only 1662 iterations, condition 84919
>>
>> nn-cg on 2 nodes 229 iterations, condition 6285
>> nn-cg on 4 nodes 331 iterations, condition 13312
>>
>> or is it not to expect, that nn-cg is faster than ilu-cg?
>>
>> cheers,
>>
>> ando
>>
>> -- 
>> /"\                               Grassl Andreas
>> \ /    ASCII Ribbon Campaign      Uni Innsbruck Institut f. Mathematik
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> 

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